Bluetooth device tree configuration

Article purpose

This article explains how to configure Bluetooth when the peripheral (or peripheral associated to the framework) is assigned to the Linux^® OS.

The configuration is performed using the device tree mechanism .

The Bluetooth companion chip chosen on our platform is a Cypress chip

Bluetooth DT bindings documentation

The Bluetooth tree bindings are composed of:

• STM32 USART device tree bindings
• The Cypress device, used as child node of the host USART device to which the slave device is attached.

Bluetooth DT configuration

This hardware description is a combination of the STM32 microprocessor device tree files (.dtsi extension) and board device tree files (.dts extension). See the device tree for an explanation of the device tree file split.

Bluetooth DT configuration (STM32 level)

The USART peripheral node is located in stm32mp157c.dtsi

• This is a set of properties that may not vary for given STM32 device, such as: registers address, clock, reset...

The USART DT configuration is explained in Serial TTY device tree configuration

Bluetooth DT configuration (board level)

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For ecosystem release v1.1.0{{#set:Ecosystem release=revision of a previous flow 1.1.0}} :
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&usart2 {
       ... 
       st,hw-flow-ctrl;                                       /* enable hardware flow control */
       ...
       bluetooth {                                            /* node of Bluetooth companion chip */         
               shutdown-gpios = <&gpioz 6 GPIO_ACTIVE_HIGH>;  /* GPIO specifier, used to enable the BT module */
               compatible = "brcm,bcm43438-bt";
               max-speed = <3000000>;
       };
};

Specific properties for USART:

• st,hw-flow-ctrl: bool flag to enable hardware flow control

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&usart2 {
       ... 
       st,hw-flow-ctrl;                            /* enable hardware flow control */
       ...
       bluetooth {                                 /* node of Bluetooth companion chip */
               pinctrl-names = "default";          
               pinctrl-0 = <&btreg>;               /* GPIO to power up or down the internal companion chip regulators */
               compatible = "brcm,bcm43438-bt";
               max-speed = <3000000>;
       };
};

Specific properties for USART:

• btreg: GPIO to power up or down the internal CYW4343W regulators used by the Bluetooth section
• st,hw-flow-ctrl: bool flag to enable hardware flow control

How to configure Bluetooth using CubeMX

The STM32CubeMX tool can be used to configure the STM32MPU device and get the corresponding platform configuration device tree files.
The STM32CubeMX may not support all the properties described in the above DT bindings documentation paragraph. If so, the tool inserts user sections in the generated device tree. These sections can then be edited to add some properties and they are preserved from one generation to another. Refer to STM32CubeMX user manual for further information.

References